DETROIT -- General Motors will beef up its lineup of small sport wagons with at least two unibody vehicles in 2008.

Company, industry and supplier sources say GM is developing vehicles for Chevrolet and Saturn. They would face established rivals such as the Toyota RAV4, Honda CR-V and Ford Escape. GM is considering a similar vehicle for Buick.

The small sport wagons will debut late in 2008 as 2009 models on an architecture referred to internally as "sub-Theta." They are under development in the United States, with help from GM Daewoo Auto & Technology.

Theta is the architecture for GM's current front-wheel-drive sport wagons, such as the Chevrolet Equinox and Saturn Vue. GM's newest offerings would be smaller than current Thetas, which are larger than the RAV4 and CR-V.

GM's decision likely is a response to the growing number of small sport wagons offered by Asian automakers.

The Asians have had a strong presence in the segment since the 1996 U.S. debut of the RAV4. The Honda CR-V hit the market a year later.

Since then, the market for RAV4-sized sport wagons has become more competitive. Hyundai introduced the Tucson last year. The Chrysler group is developing a car-based Jeep that will debut next year. Volkswagen is expected to introduce a sport wagon based on the Golf in the 2008 model year.

Ford sold 183,430 units of the Escape last year, an increase from the 167,678 units sold in 2003. Honda sold 149,281 units of the CR-V last year. Saturn sold 86,957 Vues in 2004.

GM uses the term "architecture" to signify a set of common components, performance characteristics, a common manufacturing process and a range of dimensions and connecting points for key component systems.